Reacción a "Reactions: The lineage of the so-called 'swine flu' has passed from humans to pigs almost 400 times since 2009"

Since the start of the H1N1 influenza A (pdm2009) pandemic, numerous cases of transmission of this pandemic virus from humans to pigs (reverse zoonosis) have been documented in Europe and the USA. The vast majority of these infections occurred during the years since the pandemic, when the virus circulated in humans with its highest incidence, but transmission events have not stopped since then. This study describes the frequency of these human-to-pig transmission episodes in the US from the emergence of the 2009 pandemic to the present. The introduction and establishment of new viruses of human origin in pigs increases the heterogeneity of the viruses in this species and increases the chances of the origin of swine flu strains capable of inverse transmission to humans and causing new pandemics.

Similarly, a study carried out in our INIA-CSIC laboratory demonstrated the existence of at least three genetically different lines of the human H1N1pdm2009 virus in our pig herd, the result of independent transmissions of viruses of human origin. Once introduced into swine, the new H1N1pdm2009 viruses evolved independently from their human relatives through mutation and genetic exchange with other swine influenza viruses, giving rise to a wide diversity of influenza A viruses in our swine herd. Human influenza vaccines may partially protect against some of these swine viral variants depending on the degree of antigenic similarity.

Prior to the 2009 pandemic, there were also several cases of reverse zoonoses that contributed to shaping the genetic makeup of contemporary swine influenza viruses. This evolutionary closeness between swine and human influenza viruses explains the relative ease of reciprocal transmission of viruses between the two species. For this reason, close and constant surveillance of influenza viruses in both species is absolutely necessary to anticipate possible emergencies of swine flu viruses with pandemic potential and the reissue of another pandemic similar to or with worse consequences than the one suffered in 2009.

Special surveillance should be carried out on those people who, for professional reasons, have close and frequent contact with pigs: farmers, veterinarians, butchers, transporters, etc.